Monasteries on rock pillars, once accessible only by frayed ropes.

These caves secretly held national treasures during World War II.

Where commuters walk through remnants of an ancient Greek necropolis.

An ancient octagonal weather station named for the eight Greek gods of wind.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.

The secret medieval communication system will whisk your words above the noise of the crowd.

One of the world’s smallest bars, just 13 square feet, is brimming with speakeasy flair.

This giant middle finger statue sends an unambiguous message to Italy's bankers.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

A Milanese café entirely designed by the American director Wes Anderson.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

This massive blockhead sculpture hides an entire library.

Unable to build support structures on glaciers, the engineers for this tramway were forced to design a unique system.

The video game-themed street art first popped up in the French city.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

An abandoned colonial French prison notorious for its hellish conditions.

The world's widest single drop waterfall, and the two men who legend says went over its edge in a boat.

These small, triangular, colorful houses are a staple of Madeira Island.

This otherwise ordinary close on the Royal Mile constituted the end of the world for Edinburgh’s poorest residents.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

This abandoned church in central Lyon is missing its front stairs.